Color electro-optic displays, and processes for the production thereof

ABSTRACT

A color filter array is provided in an electro-optic display by ink jet printing a plurality of colored areas ( 22 R,  22 G,  22 B) on one surface of a layer of electro-optic material ( 12 ), an adhesive layer or a protective layer. Alternatively, the ink jet printing may be effected on the same layers in various sub-assemblies used to produce electro-optic displays.

REFERENCE TO RELATED APPLICATIONS

This application claims benefit of Application Ser. No. 60/825,933,filed Sep. 18, 2006.

This application is also a continuation-in-part of copending applicationSer. No. 11/550,114, filed Oct. 17, 2006 (Publication No. 2007/0109219),which itself claims benefit of Application Ser. No. 60/596,743, filedOct. 18, 2005, and of Application Ser. No. 60/596,799, filed Oct. 21,2005.

This application is also related to:

-   -   (a) application Ser. No. 10/249,957, filed May 22, 2003 (now        U.S. Pat. No. 6,982,178), which claims benefit of Application        Ser. No. 60/319,300, filed Jun. 10, 2002, and Application Ser.        No. 60/320,186, filed May 12, 2003;    -   (b) application Ser. No. 10/907,065, filed Mar. 18, 2005 (now        U.S. Pat. No. 7,236,292), which is a divisional of the        aforementioned application Ser. No. 10/249,957;    -   (c) copending application Ser. No. 11/747,546, filed May 11,        2007, which is a continuation of the aforementioned application        Ser. No. 10/907,065;    -   (d) copending application Ser. No. 10/605,024, filed Sep. 2,        2003 (Publication No. 2004/0155857);    -   (e) application Ser. No. 10/904,063, filed Oct. 21, 2004 (now        U.S. Pat. No. 7,110,164), which is a continuation-in-part of the        aforementioned application Ser. No. 10/605,024.    -   (f) application Ser. No. 10/145,861, filed May 13, 2002 (now        U.S. Pat. No. 6,864,875), which is a continuation of application        Ser. No. 09/436,303, filed Nov. 8, 1999 (now abandoned), which        is itself a divisional of application Ser. No. 09/289,507, filed        Apr. 9, 1999 (now U.S. Pat. No. 7,075,502).

The entire contents of these copending applications, and of all otherU.S. patents and published and copending applications mentioned below,are herein incorporated by reference.

BACKGROUND OF INVENTION

The present invention relates to color electro-optic displays andprocesses for the production thereof. This invention relates to suchdisplays and processes containing an electro-optic medium which is asolid (such displays may hereinafter for convenience be referred to as“solid electro-optic displays”), in the sense that the electro-opticmedium has solid external surfaces, although the medium may, and oftendoes, have internal liquid- or gas-filled spaces, and to methods forassembling displays using such an electro-optic medium. Thus, the term“solid electro-optic displays” includes encapsulated electrophoreticdisplays and other types of displays discussed below.

The term “electro-optic”, as applied to a material or a display, is usedherein in its conventional meaning in the imaging art to refer to amaterial having first and second display states differing in at leastone optical property, the material being changed from its first to itssecond display state by application of an electric field to thematerial. Although the optical property is typically color perceptibleto the human eye, it may be another optical property, such as opticaltransmission, reflectance, luminescence or, in the case of displaysintended for machine reading, pseudo-color in the sense of a change inreflectance of electromagnetic wavelengths outside the visible range.

The terms “bistable” and “bistability” are used herein in theirconventional meaning in the art to refer to displays comprising displayelements having first and second display states differing in at leastone optical property, and such that after any given element has beendriven, by means of an addressing pulse of finite duration, to assumeeither its first or second display state, after the addressing pulse hasterminated, that state will persist for at least several times, forexample at least four times, the minimum duration of the addressingpulse required to change the state of the display element. It is shownin U.S. Pat. No. 7,170,670 that some particle-based electrophoreticdisplays capable of gray scale are stable not only in their extremeblack and white states but also in their intermediate gray states, andthe same is true of some other types of electro-optic displays. Thistype of display is properly called “multi-stable” rather than bistable,although for convenience the term “bistable” may be used herein to coverboth bistable and multi-stable displays.

Several types of electro-optic displays are known. One type ofelectro-optic display is a rotating bichromal member type as described,for example, in U.S. Pat. Nos. 5,808,783; 5,777,782; 5,760,761;6,054,071 6,055,091; 6,097,531; 6,128,124; 6,137,467; and 6,147,791(although this type of display is often referred to as a “rotatingbichromal ball” display, the term “rotating bichromal member” ispreferred as more accurate since in some of the patents mentioned abovethe rotating members are not spherical). Such a display uses a largenumber of small bodies (typically spherical or cylindrical) which havetwo or more sections with differing optical characteristics, and aninternal dipole. These bodies are suspended within liquid-filledvacuoles within a matrix, the vacuoles being filled with liquid so thatthe bodies are free to rotate. The appearance of the display is changedby applying an electric field thereto, thus rotating the bodies tovarious positions and varying which of the sections of the bodies isseen through a viewing surface. This type of electro-optic medium istypically bistable.

Another type of electro-optic display is an electro-wetting displaydeveloped by Philips and described in Hayes, R. A., et al., “Video-SpeedElectronic Paper Based on Electrowetting”, Nature, 425, 383-385 (2003).It is shown in copending application Ser. No. 10/711,802, filed Oct. 6,2004 (Publication No. 2005/0151709), that such electro-wetting displayscan be made bistable.

Another type of electro-optic display, which has been the subject ofintense research and development for a number of years, is theparticle-based electrophoretic display, in which a plurality of chargedparticles move through a fluid under the influence of an electric field.Electrophoretic displays can have attributes of good brightness andcontrast, wide viewing angles, state bistability, and low powerconsumption when compared with liquid crystal displays. Nevertheless,problems with the long-term image quality of these displays haveprevented their widespread usage. For example, particles that make upelectrophoretic displays tend to settle, resulting in inadequateservice-life for these displays.

As noted above, electrophoretic media require the presence of a fluid.In most prior art electrophoretic media, this fluid is a liquid, butelectrophoretic media can be produced using gaseous fluids; see, forexample, Kitamura, T., et al., “Electrical toner movement for electronicpaper-like display”, IDW Japan, 2001, Paper HCS1-1, and Yamaguchi, Y.,et al., “Toner display using insulative particles chargedtriboelectrically”, IDW Japan, 2001, Paper AMD4-4). See also U.S. PatentPublication No. 2005/0001810; European Patent Applications 1,462,847;1,482,354; 1,484,635; 1,500,971; 1,501,194; 1,536,271; 1,542,067;1,577,702; 1,577,703; and 1,598,694; and International Applications WO2004/090626; WO 2004/079442; and WO 2004/001498. Such gas-basedelectrophoretic media appear to be susceptible to the same types ofproblems due to particle settling as liquid-based electrophoretic media,when the media are used in an orientation which permits such settling,for example in a sign where the medium is disposed in a vertical plane.Indeed, particle settling appears to be a more serious problem ingas-based electrophoretic media than in liquid-based ones, since thelower viscosity of gaseous suspending fluids as compared with liquidones allows more rapid settling of the electrophoretic particles.

Numerous patents and applications assigned to or in the names of theMassachusetts Institute of Technology (MIT) and E Ink Corporation haverecently been published describing encapsulated electrophoretic media.Such encapsulated media comprise numerous small capsules, each of whichitself comprises an internal phase containing electrophoretically-mobileparticles suspended in a liquid suspending medium, and a capsule wallsurrounding the internal phase. Typically, the capsules are themselvesheld within a polymeric binder to form a coherent layer positionedbetween two electrodes. Encapsulated media of this type are described,for example, in U.S. Pat. Nos. 5,930,026; 5,961,804; 6,017,584;6,067,185; 6,118,426; 6,120,588; 6,120,839; 6,124,851; 6,130,773;6,130,774; 6,172,798; 6,177,921; 6,232,950; 6,249,271; 6,252,564;6,262,706; 6,262,833; 6,300,932; 6,312,304; 6,312,971; 6,323,989;6,327,072; 6,376,828; 6,377,387; 6,392,785; 6,392,786; 6,413,790;6,422,687; 6,445,374; 6,445,489; 6,459,418; 6,473,072; 6,480,182;6,498,114; 6,504,524; 6,506,438; 6,512,354; 6,515,649; 6,518,949;6,521,489; 6,531,997; 6,535,197; 6,538,801; 6,545,291; 6,580,545;6,639,578; 6,652,075; 6,657,772; 6,664,944; 6,680,725; 6,683,333;6,704,133; 6,710,540; 6,721,083; 6,724,519; 6,727,881; 6,738,050;6,750,473; 6,753,999; 6,816,147; 6,819,471; 6,822,782; 6,825,068;6,825,829; 6,825,970; 6,831,769; 6,839,158; 6,842,167; 6,842,279;6,842,657; 6,864,875; 6,865,010; 6,866,760; 6,870,661; 6,900,851;6,922,276; 6,950,200; 6,958,848; 6,967,640; 6,982,178; 6,987,603;6,995,550; 7,002,728; 7,012,600; 7,012,735; 7,023,420; 7,030,412;7,030,854; 7,034,783; 7,038,655; 7,061,663; 7,071,913; 7,075,502;7,075,703; 7,079,305; 7,106,296; 7,109,968; 7,110,163; 7,110,164;7,116,318; 7,116,466; 7,119,759; 7,119,772; 7,148,128; 7,167,155;7,170,670; 7,173,752; 7,176,880; 7,180,649; 7,190,008; 7,193,625;7,202,847; 7,202,991; 7,206,119; 7,223,672; 7,230,750; 7,230,751;7,236,790; and 7,236,792; and U.S. Patent Applications Publication Nos.2002/0060321; 2002/0090980; 2003/0011560; 2003/0102858; 2003/0151702;2003/0222315; 2004/0094422; 2004/0105036; 2004/0112750; 2004/0119681;2004/0136048; 2004/0155857; 2004/0180476; 2004/0190114; 2004/0196215;2004/0226820; 2004/0257635; 2004/0263947; 2005/0000813; 2005/0007336;2005/0012980; 2005/0017944; 2005/0018273; 2005/0024353; 2005/0062714;2005/0067656; 2005/0099672; 2005/0122284; 2005/0122306; 2005/0122563;2005/0134554; 2005/0151709; 2005/0152018; 2005/0156340; 2005/0179642;2005/0190137; 2005/0212747; 2005/0213191; 2005/0219184; 2005/0253777;2005/0280626; 2006/0007527; 2006/0024437; 2006/0038772; 2006/0139308;2006/0139310; 2006/0139311; 2006/0176267; 2006/0181492; 2006/0181504;2006/0194619; 2006/0197736; 2006/0197737; 2006/0197738; 2006/0202949;2006/0223282; 2006/0232531; 2006/0245038; 2006/0256425; 2006/0262060;2006/0279527; 2006/0291034; 2007/0035532; 2007/0035808; 2007/0052757;2007/0057908; 2007/0069247; 2007/0085818; 2007/0091417; 2007/0091418;2007/0097489; 2007/0109219; 2007/0128352; and 2007/0146310; andInternational Applications Publication Nos. WO 00/38000; WO 00/36560; WO00/67110; and WO 01/07961; and European Patents Nos. 1,099,207 B1; and1,145,072 B1.

Many of the aforementioned patents and applications recognize that thewalls surrounding the discrete microcapsules in an encapsulatedelectrophoretic medium could be replaced by a continuous phase, thusproducing a so-called polymer-dispersed electrophoretic display, inwhich the electrophoretic medium comprises a plurality of discretedroplets of an electrophoretic fluid and a continuous phase of apolymeric material, and that the discrete droplets of electrophoreticfluid within such a polymer-dispersed electrophoretic display may beregarded as capsules or microcapsules even though no discrete capsulemembrane is associated with each individual droplet; see for example,the aforementioned U.S. Pat. No. 6,866,760. Accordingly, for purposes ofthe present application, such polymer-dispersed electrophoretic mediaare regarded as sub-species of encapsulated electrophoretic media.

A related type of electrophoretic display is a so-called “microcellelectrophoretic display”. In a microcell electrophoretic display, thecharged particles and the fluid are not encapsulated withinmicrocapsules but instead are retained within a plurality of cavitiesformed within a carrier medium, typically a polymeric film. See, forexample, U.S. Pat. Nos. 6,672,921 and 6,788,449, both assigned to SipixImaging, Inc.

Although electrophoretic media are often opaque (since, for example, inmany electrophoretic media, the particles substantially blocktransmission of visible light through the display) and operate in areflective mode, many electrophoretic displays can be made to operate ina so-called “shutter mode” in which one display state is substantiallyopaque and one is light-transmissive. See, for example, theaforementioned U.S. Pat. Nos. 6,130,774 and 6,172,798, and U.S. Pat.Nos. 5,872,552; 6,144,361; 6,271,823; 6,225,971; and 6,184,856.Dielectrophoretic displays, which are similar to electrophoreticdisplays but rely upon variations in electric field strength, canoperate in a similar mode; see U.S. Pat. No. 4,418,346. Other types ofelectro-optic displays may also be capable of operating in shutter mode.

An encapsulated electrophoretic display typically does not suffer fromthe clustering and settling failure mode of traditional electrophoreticdevices and provides further advantages, such as the ability to print orcoat the display on a wide variety of flexible and rigid substrates.(Use of the word “printing” is intended to include all forms of printingand coating, including, but without limitation: pre-metered coatingssuch as patch die coating, slot or extrusion coating, slide or cascadecoating, curtain coating; roll coating such as knife over roll coating,forward and reverse roll coating; gravure coating; dip coating; spraycoating; meniscus coating; spin coating; brush coating; air knifecoating; silk screen printing processes; electrostatic printingprocesses; thermal printing processes; ink jet printing processes;electrophoretic deposition (See US Patent Publication No. 2004/0226820);and other similar techniques.) Thus, the resulting display can beflexible. Further, because the display medium can be printed (using avariety of methods), the display itself can be made inexpensively.

Other types of electro-optic media may also be used in the displays ofthe present invention.

An electrophoretic display normally comprises a layer of electrophoreticmaterial and at least two other layers disposed on opposed sides of theelectrophoretic material, one of these two layers being an electrodelayer. In most such displays both the layers are electrode layers, andone or both of the electrode layers are patterned to define the pixelsof the display. For example, one electrode layer may be patterned intoelongate row electrodes and the other into elongate column electrodesrunning at right angles to the row electrodes, the pixels being definedby the intersections of the row and column electrodes. Alternatively,and more commonly, one electrode layer has the form of a singlecontinuous electrode and the other electrode layer is patterned into amatrix of pixel electrodes, each of which defines one pixel of thedisplay. In another type of electrophoretic display, which is intendedfor use with a stylus, print head or similar movable electrode separatefrom the display, only one of the layers adjacent the electrophoreticlayer comprises an electrode, the layer on the opposed side of theelectrophoretic layer typically being a protective layer intended toprevent the movable electrode damaging the electrophoretic layer.

The manufacture of a three-layer electro-optic display normally involvesat least one lamination operation. For example, in several of theaforementioned MIT and E Ink patents and applications, there isdescribed a process for manufacturing an encapsulated electrophoreticdisplay in which an encapsulated electrophoretic medium comprisingcapsules in a binder is coated on to a flexible substrate comprisingindium-tin-oxide (ITO) or a similar conductive coating (which acts as anone electrode of the final display) on a plastic film, thecapsules/binder coating being dried to form a coherent layer of theelectrophoretic medium firmly adhered to the substrate. Separately, abackplane, containing an array of pixel electrodes and an appropriatearrangement of conductors to connect the pixel electrodes to drivecircuitry, is prepared. To form the final display, the substrate havingthe capsule/binder layer thereon is laminated to the backplane using alamination adhesive. (A very similar process can be used to prepare anelectrophoretic display usable with a stylus or similar movableelectrode by replacing the backplane with a simple protective layer,such as a plastic film, over which the stylus or other movable electrodecan slide.) In one preferred form of such a process, the backplane isitself flexible and is prepared by printing the pixel electrodes andconductors on a plastic film or other flexible substrate. The obviouslamination technique for mass production of displays by this process isroll lamination using a lamination adhesive. Similar manufacturingtechniques can be used with other types of electro-optic displays. Forexample, a microcell electrophoretic medium or a rotating bichromalmember medium may be laminated to a backplane in substantially the samemanner as an encapsulated electrophoretic medium.

As discussed in the aforementioned U.S. Pat. No. 6,982,178, (see column3, lines 63 to column 5, line 46) many of the components used inelectrophoretic displays, and the methods used to manufacture suchdisplays, are derived from technology used in liquid crystal displays(LCD's). For example, electrophoretic displays may make use of an activematrix backplane comprising an array of transistors or diodes and acorresponding array of pixel electrodes, and a “continuous” frontelectrode (in the sense of an electrode which extends over multiplepixels and typically the whole display) on a transparent substrate,these components being essentially the same as in LCD's. However, themethods used for assembling LCD's cannot be used with encapsulatedelectrophoretic displays. LCD's are normally assembled by forming thebackplane and front electrode on separate glass substrates, thenadhesively securing these components together leaving a small aperturebetween them, placing the resultant assembly under vacuum, and immersingthe assembly in a bath of the liquid crystal, so that the liquid crystalflows through the aperture between the backplane and the frontelectrode. Finally, with the liquid crystal in place, the aperture issealed to provide the final display.

This LCD assembly process cannot readily be transferred to solidelectro-optic displays. Because the electro-optic material is solid, itmust be present between the backplane and the front electrode beforethese two integers are secured to each other. Furthermore, in contrastto a liquid crystal material, which is simply placed between the frontelectrode and the backplane without being attached to either, a solidelectro-optic medium normally needs to be secured to both; in most casesthe solid electro-optic medium is formed on the front electrode, sincethis is generally easier than forming the medium on thecircuitry-containing backplane, and the front electrode/electro-opticmedium combination is then laminated to the backplane, typically bycovering the entire surface of the electro-optic medium with an adhesiveand laminating under heat, pressure and optionally vacuum.

As discussed in the aforementioned U.S. Pat. No. 6,312,304, themanufacture of solid electro-optic displays also presents problems inthat the optical components (the electro-optic medium) and theelectronic components (in the backplane) have differing performancecriteria. For example, it is desirable for the optical components tooptimize reflectivity, contrast ratio and response time, while it isdesirable for the electronic components to optimize conductivity,voltage-current relationship, and capacitance, or to possess memory,logic, or other higher-order electronic device capabilities. Therefore,a process for manufacturing an optical component may not be ideal formanufacturing an electronic component, and vice versa. For example, aprocess for manufacturing an electronic component can involve processingunder high temperatures. The processing temperature can be in the rangefrom about 300° C. to about 600° C. Subjecting many optical componentsto such high temperatures, however, can be harmful to the opticalcomponents by degrading the electro-optic medium chemically or bycausing mechanical damage.

This patent describes a method of manufacturing an electro-optic displaycomprising providing a modulating layer including a first substrate andan electro-optic material provided adjacent the first substrate, themodulating layer being capable of changing a visual state uponapplication of an electric field; providing a pixel layer comprising asecond substrate, a plurality of pixel electrodes provided on a frontsurface of the second substrate and a plurality of contact pads providedon a rear surface of the second substrate, each pixel electrode beingconnected to a contact pad through a via extending through the secondsubstrate; providing a circuit layer including a third substrate and atleast one circuit element; and laminating the modulating layer, thepixel layer, and the circuit layer to form the electro-optic display.

Electro-optic displays are often costly; for example, the cost of thecolor LCD found in a portable computer is typically a substantialfraction of the entire cost of the computer. As the use of electro-opticdisplays spreads to devices, such as cellular telephones and personaldigital assistants (PDA's), much less costly than portable computers,there is great pressure to reduce the costs of such displays. Theability to form layers of some solid electro-optic media by printingtechniques on flexible substrates, as discussed above, opens up thepossibility of reducing the cost of electro-optic components of displaysby using mass production techniques such as roll-to-roll coating usingcommercial equipment used for the production of coated papers, polymericfilms and similar media. However, such equipment is costly and the areasof electro-optic media presently sold may be insufficient to justifydedicated equipment, so that it may typically be necessary to transportthe coated medium from a commercial coating plant to the plant used forfinal assembly of electro-optic displays without damage to therelatively fragile layer of electro-optic medium.

Also, most prior art methods for final lamination of electrophoreticdisplays are essentially batch methods in which the electro-opticmedium, the lamination adhesive and the backplane are only broughttogether immediately prior to final assembly, and it is desirable toprovide methods better adapted for mass production.

The aforementioned U.S. Pat. No. 6,982,178 describes a method ofassembling a solid electro-optic display (including an encapsulatedelectrophoretic display) which is well adapted for mass production.Essentially, this patent describes a so-called “front plane laminate”(“FPL”) which comprises, in order, a light-transmissiveelectrically-conductive layer; a layer of a solid electro-optic mediumin electrical contact with the electrically-conductive layer; anadhesive layer; and a release sheet. Typically, the light-transmissiveelectrically-conductive layer will be carried on a light-transmissivesubstrate, which is preferably flexible, in the sense that the substratecan be manually wrapped around a drum (say) 10 inches (254 mm) indiameter without permanent deformation. The term “light-transmissive” isused in this patent and herein to mean that the layer thus designatedtransmits sufficient light to enable an observer, looking through thatlayer, to observe the change in display states of the electro-opticmedium, which will normally be viewed through theelectrically-conductive layer and adjacent substrate (if present); incases where the electro-optic medium displays a change in reflectivityat non-visible wavelengths, the term “light-transmissive” should ofcourse be interpreted to refer to transmission of the relevantnon-visible wavelengths. The substrate will typically be a polymericfilm, and will normally have a thickness in the range of about 1 toabout 25 mil (25 to 634 μm), preferably about 2 to about 10 mil (51 to254 μm). The electrically-conductive layer is conveniently a thin metalor metal oxide layer of, for example, aluminum or ITO, or may be aconductive polymer. Poly(ethylene terephthalate) (PET) films coated withaluminum or ITO are available commercially, for example as “aluminizedMylar” (“Mylar” is a Registered Trade Mark) from E.I. du Pont de Nemours& Company, Wilmington Del., and such commercial materials may be usedwith good results in the front plane laminate.

Assembly of an electro-optic display using such a front plane laminatemay be effected by removing the release sheet from the front planelaminate and contacting the adhesive layer with the backplane underconditions effective to cause the adhesive layer to adhere to thebackplane, thereby securing the adhesive layer, layer of electro-opticmedium and electrically-conductive layer to the backplane. This processis well-adapted to mass production since the front plane laminate may bemass produced, typically using roll-to-roll coating techniques, and thencut into pieces of any size needed for use with specific backplanes.

The aforementioned U.S. Pat. No. 6,982,178 also describes a method fortesting the electro-optic medium in a front plane laminate prior toincorporation of the front plane laminate into a display. In thistesting method, the release sheet is provided with an electricallyconductive layer, and a voltage sufficient to change the optical stateof the electro-optic medium is applied between this electricallyconductive layer and the electrically conductive layer on the opposedside of the electro-optic medium. Observation of the electro-opticmedium will then reveal any faults in the medium, thus avoidinglaminating faulty electro-optic medium into a display, with theresultant cost of scrapping the entire display, not merely the faultyfront plane laminate.

The aforementioned U.S. Pat. No. 6,982,178 also describes a secondmethod for testing the electro-optic medium in a front plane laminate byplacing an electrostatic charge on the release sheet, thus forming animage on the electro-optic medium. This image is then observed in thesame way as before to detect any faults in the electro-optic medium.

The aforementioned 2004/0155857 describes a so-called “double releasesheet” which is essentially a simplified version of the front planelaminate of the aforementioned U.S. Pat. No. 6,982,178. One form of thedouble release sheet comprises a layer of a solid electro-optic mediumsandwiched between two adhesive layers, one or both of the adhesivelayers being covered by a release sheet. Another form of the doublerelease sheet comprises a layer of a solid electro-optic mediumsandwiched between two release sheets. Both forms of the double releasefilm are intended for use in a process generally similar to the processfor assembling an electro-optic display from a front plane laminatealready described, but involving two separate laminations; typically, ina first lamination the double release sheet is laminated to a frontelectrode to form a front sub-assembly, and then in a second laminationthe front sub-assembly is laminated to a backplane to form the finaldisplay, although the order of these two laminations could be reversedif desired.

The aforementioned copending application Ser. No. 11/550,114 describes aso-called “inverted front plane laminate”, which is a variant of thefront plane laminate described in the aforementioned U.S. Pat. No.6,982,178. This inverted front plane laminate comprises, in order, atleast one of a light-transmissive protective layer and alight-transmissive electrically-conductive layer; an adhesive layer; alayer of a solid electro-optic medium; and a release sheet. Thisinverted front plane laminate is used to form an electro-optic displayhaving a layer of lamination adhesive between the electro-optic layerand the front electrode or front substrate; a second, typically thinlayer of adhesive may or may not be present between the electro-opticlayer and a backplane. Such electro-optic displays can combine goodresolution with good low temperature performance. This copendingapplication also describes coloring the layer of lamination adhesivebetween the electro-optic layer and the front electrode to form a colorfilter.

Most types of electro-optic media have only a limited number of opticalstates, for example a dark (black) state, a light (white) state and, insome cases, one or more intermediate gray states. Accordingly, toconstruct a full color display using such media, it is common practiceto place an electro-optic medium adjacent a color filter having, forexample, multiple red, green and blue areas, and to provide a drivingarrangement for the electro-optic medium which permits independentcontrol of the medium adjacent each red, green or blue area. Certainapplications of color filters with electrophoretic displays aredescribed in the aforementioned U.S. Pat. No. 6,864,875. Theaforementioned 2003/0011560 describes ways for modifying the opticalproperties of electrophoretic displays by incorporating an opticalbiasing element in any one of several components of the display.

Choosing the optimum method for providing a color filter array in anelectro-optic display is more complex than it might at first appear, andinvolves a number of often-conflicting desiderata. It is desirable tokeep the color filter array as close to the electro-optic layer aspossible, since any significant spacing between the two may lead toparallax, which in turn can distort the colors seen when the display isviewed off-axis (i.e., in a direction other than perpendicular to theviewing surface). However, it is also necessary to consider the ease ofincorporation of the color filter array into the selected positionwithin the display; for example, it is relatively easy to attach apre-formed color filter array on to the viewing surface of the display,but it may be substantially more difficult to place a color filter arraybetween two interior layers of the display. In addition, the coloredareas of the color filter array need to be aligned with the pixelelectrodes on the backplane of the display to ensure that, for example,a pixel which is supposed to show red when the electro-optic medium isin a white optical state does not show a mixture of red and blue, thusgravely distorting the intended colors of the image. In this regard, itshould be noted that thin front plane laminates (including invertedfront plane laminates) and double release films tend to change sizeslightly during laminations, and even a small change in size can havesevere effects on the electro-optic performance of the resultingdisplay. For example, if a backplane has 500 pixels per row, and a frontplane laminate provided with a color filter array accurately spaced toalign with the pixels changes its dimensions by 0.1 percent duringlamination, if the front plane laminate is accurately aligned with thepixels at one end of the row, it will be mis-aligned by one-half of apixel at the other end, with severe degradation of the color image atthis other end of the row. Finally, there is a need to consider the typeof display being produced; many types of color filter arrays, forexample glass-based arrays, are too rigid for incorporation intoflexible displays.

It has now been discovered that useful color filter arrays can beproduced by ink jet printing colored areas on to various surfaces of anelectro-optic display, or the corresponding surfaces of a front planelaminate, inverted front plane laminate or double release film used toproduce such a display, and this invention relates to this process andto the products thereof.

SUMMARY OF THE INVENTION

In one aspect, this invention provides a (first) process for preparing alayer of electro-optic material having a color filter array thereon,which process comprises ink jet printing a plurality of colored areas onone surface of the layer of electro-optic material.

This first process of the present invention may hereinafter forconvenience be called the “electro-optic layer printing” or “EOLP”process of the invention. Typically, this process will be used to printa full color filter array having two, three or four colors, althoughmore colors can be used if desired. Thus, in a typical EOLP process, aplurality of first colored areas and a plurality of second colored areasare printed on the surface of the layer of electro-optic material, thefirst and second colored areas being of different colors.

The EOLP process may be used with any of the types of electro-opticmaterials discussed above. Thus, for example, in the EOLP process, theelectro-optic material may comprise a rotating bichromal member materialor a microcell electrophoretic material. Alternatively, theelectro-optic material may comprise an encapsulated electrophoreticmaterial comprising a plurality of capsules in a binder, or apolymer-dispersed electrophoretic material. The ink used may beradiation curable, so that after the ink has been printed it is exposedto radiation effective to cure the ink. Alternatively, the ink used maybe solvent-based, that is to say may comprise pigment particles in anorganic solvent.

The EOLP process may be carried out while the layer of electro-opticmaterial is disposed on a backplane comprising at least one pixelelectrode. The EOLP process may include the additional step oflaminating an adhesive layer over said one surface of the layer ofelectro-optic material.

In another aspect, this invention provides a layer of electro-opticmaterial having a plurality of colored areas printed on one surfacethereof. This aspect of the present invention may hereinafter forconvenience be called the “printed electro-optic layer” or “PEOL” aspectof the invention. Typically, the printed layer will be in the form of afull color filter array having two, three or four colors, although morecolors can be used if desired. Thus, a typical PEOL will have aplurality of first colored areas and a plurality of second colored areasprinted on its surface, the first and second colored areas being ofdifferent colors.

A PEOL may use any of the types of electro-optic materials discussedabove. Thus, for example, in a PEOL, the electro-optic material maycomprise a rotating bichromal member material or a microcellelectrophoretic material. Alternatively, the electro-optic material maycomprise an encapsulated electrophoretic material comprising a pluralityof capsules in a binder, or a polymer-dispersed electrophoreticmaterial.

This invention extends to a printed electro-optic layer disposed on abackplane comprising at least one pixel electrode, and to a PEOL havingan adhesive layer laminated over the printed surface of the layer ofelectro-optic material.

This invention also extends to front plane laminates, double releasefilms and inverted front plane laminates incorporating printedelectro-optic layers of the invention. Thus, this invention provides anarticle of manufacture (a front plane laminate) comprising, in order: alight-transmissive electrically-conductive layer; a layer of a solidelectro-optic medium in electrical contact with theelectrically-conductive layer; an adhesive layer; and a release sheet,wherein the layer of a solid electro-optic medium is a PEOL of thepresent invention. This invention also provides an article ofmanufacture (a double release film) comprising: a layer of a solidelectro-optic medium having first and second surfaces on opposed sidesthereof, a first adhesive layer on the first surface of the layer ofsolid electro-optic medium; a release sheet disposed on the opposed sideof the first adhesive layer from the layer of solid electro-opticmedium; and a second adhesive layer on the second surface of the layerof solid electro-optic medium, wherein the layer of a solidelectro-optic medium is a PEOL of the present invention. This inventionalso provides an article of manufacture (a double release sheet)comprising: a layer of a solid electro-optic medium having first andsecond surfaces on opposed sides thereof, a first release sheet coveringthe first surface of the layer of solid electro-optic medium; and asecond release sheet covering the second surface of the layer of solidelectro-optic medium, wherein the layer of a solid electro-optic mediumis a PEOL of the present invention. Finally, this invention provides anarticle of manufacture (an inverted front plane laminate) comprising, inorder: a release sheet; a layer of a solid electro-optic medium; anadhesive layer; and at least one of a light-transmissive protectivelayer and a light-transmissive electrically-conductive layer, whereinthe layer of a solid electro-optic medium is a PEOL of the presentinvention.

Another major aspect of the present invention relates to printing ofcolored areas on adhesive layers, desirably adhesive layers alreadyassociated with electro-optic layers. Thus, this invention provides aprocess for preparing a sub-assembly useful for forming a colorelectro-optic display, the process comprising providing a sub-assemblycomprising a layer of electro-optic material and an adhesive layerhaving an exposed surface, and ink jet printing a plurality of coloredareas on the exposed surface of the adhesive layer.

This aspect of the present invention may hereinafter for convenience becalled the “adhesive layer printing” or “ALP” aspect of the invention.Typically, this process will be used to print a full color filter arrayhaving two, three or four colors, although more colors can be used ifdesired. Thus, in a typical ALP process, a plurality of first coloredareas and a plurality of second colored areas are printed on the surfaceof the layer of electro-optic material, the first and second coloredareas being of different colors.

The ALP process may be used with any of the types of electro-opticmaterials discussed above. Thus, for example, in the ALP process, theelectro-optic material may comprise a rotating bichromal member materialor a microcell electrophoretic material. Alternatively, theelectro-optic material may comprise an encapsulated electrophoreticmaterial comprising a plurality of capsules in a binder, or apolymer-dispersed electrophoretic material. The ink used may beradiation curable, so that after the ink has been printed it is exposedto radiation effective to cure the ink. Alternatively, the ink used maybe solvent-based, that is to say may comprise pigment particles in anorganic solvent.

The ALP process may be carried out with the layer of electro-opticmaterial disposed on a backplane comprising at least one pixelelectrode, with the adhesive layer being disposed on the opposed side ofthe layer of electro-optic material from the backplane.

This invention extends to color printed adhesive layers such as thoseproduced by the ALP process. Thus, this invention extends to asub-assembly useful for forming a color electro-optic display, thesub-assembly comprising a layer of electro-optic material and anadhesive layer, the adhesive layer having a plurality of colored areasprinted on one surface thereof.

This aspect of the present invention may hereinafter for convenience becalled the “printed adhesive layer sub-assembly” or “PALSA” aspect ofthe invention. Typically, the printed adhesive layer will be in the formof a full color filter array having two, three or four colors, althoughmore colors can be used if desired. Thus, a typical PALSA will have aplurality of first colored areas and a plurality of second colored areasprinted on its surface, the first and second colored areas being ofdifferent colors. The plurality of colored areas may be printed on thesurface of the adhesive layer remote from the layer of electro-opticmaterial or on the surface of the adhesive layer adjacent the layer ofelectro-optic material.

A PALSA may use any of the types of electro-optic materials discussedabove. Thus, for example, in a PALSA, the electro-optic material maycomprise a rotating bichromal member material or a microcellelectrophoretic material. Alternatively, the electro-optic material maycomprise an encapsulated electrophoretic material comprising a pluralityof capsules in a binder, or a polymer-dispersed electrophoreticmaterial.

This invention extends to a PALSA disposed on a backplane comprising atleast one pixel electrode, and to a PALSA having a second adhesive layerlaminated over the surface of the layer of electro-optic material remotefrom the adhesive layer bearing the plurality of colored areas.

A PALSA can form part of a front plane laminate, double release film orinverted front plane laminate. Thus, this invention provides an articleof manufacture (a front plane laminate) comprising, in order: alight-transmissive electrically-conductive layer; a layer of a solidelectro-optic medium in electrical contact with theelectrically-conductive layer; an adhesive layer; and a release sheet,wherein the layer of the solid electro-optic medium and the adhesivelayer form a PALSA of the present invention. This invention alsoprovides an article of manufacture (a double release film) comprising: alayer of a solid electro-optic medium having first and second surfaceson opposed sides thereof, a first adhesive layer on the first surface ofthe layer of solid electro-optic medium; a release sheet disposed on theopposed side of the first adhesive layer from the layer of solidelectro-optic medium; and a second adhesive layer on the second surfaceof the layer of solid electro-optic medium, wherein one of the adhesivelayers has a plurality of colored areas printed thereon. Finally, thisinvention provides an article of manufacture (an inverted front planelaminate) comprising, in order: a release sheet; a layer of a solidelectro-optic medium; an adhesive layer; and at least one of alight-transmissive protective layer and a light-transmissiveelectrically-conductive layer, wherein the layer of the solidelectro-optic medium and the adhesive layer form a PALSA of the presentinvention.

A third major aspect of the present invention relates to printingcolored areas on the protective layers (also often referred to as “frontsubstrates”) of electro-optic displays. and sub-assemblies used forforming such displays. Thus, this invention provides a process forpreparing a color electro-optic display (or a sub-assembly which canlater be used to form such a display), the process comprising providinga film comprising a layer of electro-optic material and a protectivelayer having an exposed surface, and ink jet printing a plurality ofcolored areas on the exposed surface of the protective layer.

This aspect of the present invention may hereinafter for convenience becalled the “protective layer printing” or “PLP” aspect of the invention.Typically, this process will be used to print a full color filter arrayhaving two, three or four colors, although more colors can be used ifdesired. Thus, in a typical PLP process, a plurality of first coloredareas and a plurality of second colored areas are printed on the surfaceof the layer of electro-optic material, the first and second coloredareas being of different colors. In the PLP process, the film mayfurther comprise a light-transmissive electrically conductive layerdisposed between the protective layer and the layer of electro-opticmaterial. Also, in a PLP process, prior to printing of the ink, theexposed surface of the protective layer may be coated with an inkreceiving medium for enhancing the adhesion of the ink to the protectivesheet.

The PLP process may be used with any of the types of electro-opticmaterials discussed above. Thus, for example, in the PLP process, theelectro-optic material may comprise a rotating bichromal member materialor a microcell electrophoretic material. Alternatively, theelectro-optic material may comprise an encapsulated electrophoreticmaterial comprising a plurality of capsules in a binder, or apolymer-dispersed electrophoretic material. The ink used may beradiation curable, so that after the ink has been printed it is exposedto radiation effective to cure the ink. Alternatively, the ink used maybe solvent-based, that is to say may comprise pigment particles in anorganic solvent.

The PLP process may be carried out with the layer of electro-opticmaterial disposed on a backplane comprising at least one pixelelectrode, with the protective layer being disposed on the opposed sideof the layer of electro-optic material from the backplane.

This invention also provides a film for use in forming a colorelectro-optic display, the film comprising a layer of electro-opticmaterial and a protective layer having an exposed surface, theprotective layer having a plurality of colored areas printed on itsexposed surface.

This aspect of the present invention may hereinafter for convenience becalled the “printed protective film” or “PPF” aspect of the invention.Typically, the printed protective layer will be in the form of a fullcolor filter array having two, three or four colors, although morecolors can be used if desired. Thus, a typical PPF will have a pluralityof first colored areas and a plurality of second colored areas printedon its surface, the first and second colored areas being of differentcolors.

A PPF may use any of the types of electro-optic materials discussedabove. Thus, for example, in a PPF, the electro-optic material maycomprise a rotating bichromal member material or a microcellelectrophoretic material. Alternatively, the electro-optic material maycomprise an encapsulated electrophoretic material comprising a pluralityof capsules in a binder, or a polymer-dispersed electrophoreticmaterial. This invention extends to a PPF disposed on a backplanecomprising at least one pixel electrode, and to an article ofmanufacture (an inverted front plane laminate) comprising, in order: arelease sheet; a layer of a solid electro-optic medium; an adhesivelayer; and a light-transmissive protective layer, wherein the protectivelayer has a plurality of colored areas printed on its surface remotefrom the adhesive layer.

A fourth major aspect of the present invention relates to methods forproviding colored areas on displays at locations registered with thepixel electrodes on the backplanes of such displays. One such processfor providing printed colored areas on an electro-optic display, theprocess comprises: providing a display comprising a backplane bearing aplurality of pixel electrodes and a layer of an electro-optic materialdisposed on the backplane, the display having an exposed surface remotefrom the backplane; applying voltages to the pixel electrodes andthereby forming an image on the layer of electro-optic material;detecting the image; and ink jet printing the colored areas on theexposed surface in registry with the detected image.

This aspect of the present invention may hereinafter for convenience becalled the “registered ink jet printing” or “RIJP” aspect of theinvention. In this process, the colored areas may be printed on thelayer of electro-optic material, or on an over-layer superposed over thelayer of electro-optic material. This over-layer may be an adhesivelayer, a light-transmissive electrode or a protective layer.

Finally, this invention provides a process for placing a color filterarray on an electro-optic display, the process comprising: providing acolor filter array; providing a display comprising a backplane bearing aplurality of pixel electrodes and a layer of an electro-optic materialdisposed on the backplane, the display having an exposed surface remotefrom the backplane; applying voltages to the pixel electrodes andthereby forming an image on the layer of electro-optic material;detecting the image; and securing the color filter array on the exposedsurface in registry with the detected image. This aspect of the presentinvention may hereinafter for convenience be called the “registeredcolor filter array placement” or “RCFAP” aspect of the invention.

When printing is effected on an electro-optic material in the presentinvention and the electro-optic material is a rotating bichromal membermaterial or a microcell electrophoretic material, or in the PLP process,printing is effected on a polymer surface, and it is within the skill ofthe ink jet art to print on such polymeric surfaces. Those skilled inink jet printing will be aware of various materials (for example,hydrophilic polymers such as gelatin, poly(vinyl alcohol) andpolyvinylpyridine, or transparent microporous layers) which may beapplied to polymeric surfaces to enhance the adhesion of ink jet inksthereto or to improve print resolution, durability, and/or color densitycharacteristics. The electro-optic material used can also be anencapsulated electrophoretic material, of either the type comprising aplurality of capsules (usually in a polymeric binder) or of thepolymer-dispersed type. Rather surprisingly, it has been found that sucha capsule layer is a good receiver for ink jet inks and that at leastsome conventional ink jet colorants do not substantially interfere withthe electro-optic performance of the electro-optic material.Accordingly, any color image, including a red/green/blue,red/green/blue/white or cyan/magenta/yellow color filter array can berapidly and conveniently deposited on the electro-optic material at highresolution. The resulting modified electro-optic layer with color filterarray included can then be incorporated into an electro-optic display inany of the ways described in the aforementioned patents andapplications, including processes making use of front plane laminates,inverted front plane laminates, and double release films, as mentionedabove. Similarly, it has been found that many lamination adhesives usedin electro-optic displays can be ink jet printed in a similar mannerwith good results. With both electro-optic materials and laminationadhesives, it may be desirable to pre-treat the surfaces with materials,such as those discussed above, to improve the characteristics of theprinted ink jet image on the electro-optic material and laminationadhesive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 4 of the accompanying drawings are schematic elevationsshowing various stages in a preferred electro-optic layer printingprocess of the present invention starting from a double release film.

FIG. 5 illustrates the array of colored sub-pixels used in the preferredprotective layer printing process of the present invention described inExample 2 below.

DETAILED DESCRIPTION

As already mentioned, various aspects of the present invention make useof ink jet printing (including, possibly, so-called “solid ink jetprinting” where the ink solidifies on contact with the surface beingprinted rather than drying on this surface) to form colored areas, andtypically a color filter array, on the surface of an electro-opticmaterial, lamination adhesive or protective layer used to form anelectro-optic display. Hereinafter, the invention will mainly bedescribed with reference to the formation of three or four color filterarrays, but it should be borne in mind that the invention extends tosimpler processes involving only one or two colors, and to processesinvolving more than four colors.

Although other color printing methods could, in principle, be used inplace of ink jet printing; ink jet printing has the advantage that nocolorant donor medium actually comes in contact with the layer beingprinted. Such contact can lead to severe problems; for example, anattempt to use a dye sublimation (dye diffusion thermal transfer)printer in a modification of an electro-optic layer printing process ofthe present invention led to the welding of the electro-optic layer tothe dye donor sheet.

It will be seen from the description above that the present inventionprovides numerous different processes for the formation of color filterarrays, and the choice of which specific process is adopted will in manycases be governed by the exact structure of the electro-optic display,the thicknesses of the various layers therein, and the processes used toassemble the various layers of the display. Typically (see, for example,FIG. 10 of the aforementioned U.S. Pat. No. 6,982,178 and FIG. 3 of theaforementioned 2007/0109219), an electro-optic display comprises(reading from the viewing surface to the backplane, downwardly asillustrated in these two Figures):

-   -   (a) (optionally) barrier and other auxiliary protective layers;    -   (b) a protective layer/front substrate;    -   (c) a front electrode layer (in practice, layers (b) and (c) are        often formed from a commercial two-layer film, such as        poly(ethylene terephthalate)/indium tin oxide, so that it is not        possible for the manufacturer of an electro-optic display to        insert anything between these two layers);    -   (d) (optionally) a front adhesive layer;    -   (e) a layer of electro-optic material;    -   (f) a rear adhesive layer; and    -   (g) a backplane bearing pixel electrodes.        Since the electro-optic material is often opaque, a color filter        array must normally lie between the electro-optic layer (e) and        the viewing surface of the display. Furthermore, it is usually        desired to keep the color filter array as close to the        electro-optic layer as possible to avoid parallax problems.        Hence, it is generally undesirable to place the color filter        array (CFA) on the outside surface of layer (a) both because of        the large separation from the electro-optic layer and because of        the risk of mechanical damage to the CFA. This, there are        potentially three interfaces where the CFA can be located,        namely interfaces a/b, c/d and d/e. Furthermore, for each        interface the CFA can be formed by printing on either one of the        two adjacent layers. However, if is desired to print the CFA        already registered with the backplane, it is advantageous to        print on the layer closer to the backplane, provided that layer        is already attached to the backplane at the time printing        occurs.

It should be noted that if the CFA is printed at interface c/d or d/e,the CFA will lie between the electrodes of the display, whereas if theCFA is printed at interface a/b it will not lie between the electrodes,and the required properties of the ink used differ in the two cases. Ifthe CFA lies between the electrodes, it is important that the dielectricconstant not be too high or kickback may occur. (“Kickback” or“Self-erasing” is a phenomenon observed in some electro-optic displays(see, for example, Ota, I., et al., “Developments in ElectrophoreticDisplays”, Proceedings of the SID, 18, 243 (1977), where self-erasingwas reported in an unencapsulated electrophoretic display) whereby, whenthe voltage applied across the display is switched off, theelectro-optic medium may at least partially reverse its optical state,and in some cases a reverse voltage, which may be larger than theoperating voltage, can be observed to occur across the electrodes.)Conversely, if the CFA lies between the electrodes, it is important thatthe conductivity of the ink not be too high or blooming may occur.(“Blooming” is a phenomenon whereby the area of the electro-optic layerwhich changes optical state in response to change of voltage at a pixelelectrode is larger than the pixel electrode itself.) Humectants,non-aqueous solvents, and surfactants are commonly employed incommercial ink jet inks, and these materials can potentially interferewith the electro-optic properties of the electro-optic material, forexample by changing the conductivity of the electro-optic layer, andhence can cause unexpected behavior if present between the displayelectrodes. Also, in all processes of the present invention thecolorants in the ink should be transparent when dry, so that either dyesor very small particle pigmented inks should be used. Transparentpigmented inks are highly desirable in the present process, because suchinks will not penetrate appreciably into the electro-optic layer, and,when the electro-optic layer is an electrophoretic layer, cannotinteract unfavorably with the internal phase (electrophoretic particlesand surrounding fluid) of this electrophoretic layer. Radiation curable(typically ultraviolet curable) inks have been found very suitable foruse in the present processes, as have (organic) solvent-based pigmentinks. The latter can be formulated using very small amounts of polymericbinders so that the dried ink layer is of minimal thickness and minimaleffect on the performance of the electro-optic material. Subject to theforegoing considerations, any known type of ink jet printer can be used.Clearly, for very high resolution, good positioning and uniform inkdeposition is important.

Furthermore, as already mentioned the choice of which layer is to inkjet printed by a process of the present invention to form a CFA isgreatly affected by the “construction method” used to form the display(i.e., the order in which the various layers are assembled to form thedisplay). Three common constructions methods will now be discussed,although others will ready by apparent to those skilled in thetechnology of electro-optic displays.

Construction Method A

As described in the aforementioned U.S. Pat. No. 6,982,178, one methodcommonly used to produce electro-optic, and especially encapsulated orpolymer-dispersed electrophoretic, displays begins by coating theelectrophoretic medium on to a PET/ITO film. Separately, a laminationadhesive is coated on to a release sheet. The laminationadhesive/release sheet sub-assembly is then laminated to theelectrophoretic layer to form a front plane laminate, typically on aroll-to-roll basis. The front plane laminate is then cut to a sizeneeded for an individual display, the release sheet is removed and theremaining layers laminated to a backplane, typically a thin filmtransistor (TFT) active matrix backplane. In this process, because theelectrophoretic material layer, layer (e) above, is deposited directlyon the front substrate/front electrode layer, layers (b)/(c) above, withno intervening front adhesive layer (d), the only surface available forink jet printing is the exposed surface of the front substrate, layer(b), i.e., a PLP method of the present invention needs to be used. Inkjet printing on this surface after the front plane laminate has beenlaminated to the backplane is essentially printing on a fully-functionalactive matrix display. Thus, the display can be imaged to a fiducialpattern before printing the CFA, thus taking advantage of an RIJPprocess of the present invention and easing registration of the colorfilter array with the pixel electrodes in the backplane.

Construction Method B

Other less common methods for producing electro-optic displays offermore options for introducing a color filter array by ink jet printing.One such method is to coat the electro-optic material directly on to abackplane, separately coat lamination adhesive to a PET/ITO frontsubstrate, and laminate the two resulting sub-assemblies together. Thismethod allows ink jet printing of a CFA directly on to the electro-opticlayer before the final lamination step. Such an EOLP process of thepresent invention has an advantage that the CFA is in intimate contactwith, and hence as close as possible to, the electro-optic layer,thereby eliminating any possible light-piping or parallax problems dueto light entering through one CFA sub-pixel and leaving through adifferent sub-pixel. However, this approach does limit the choice of inkjet inks as discussed above, as the CFA is interposed between the twoelectrodes and in contact with the electro-optic layer. It also requirescoating the electro-optic material directly on to the backplane, whichis typically a batch process instead of the roll-to-roll processpossible in Construction Method A above.

A variant of the construction method described in the precedingparagraph using a double release sheet permits roll-to-roll coating ofthe electro-optic material. In this variant, the electro-optic materialis coated on to a disposable first release sheet. Separately, alamination adhesive is coated on to a second release sheet, and thelamination adhesive is laminated to the electro-optic material to form adouble release sheet having the structure first releasesheet/electro-optic material/lamination adhesive/second release sheet.The second release sheet is then removed, and the remaining layerslaminated to a backplane. The first release sheet can then be removedand a PET/ITO front substrate/front electrode laminated over theelectro-optic material to produce a final display having the optionalfront adhesive layer. As discussed in the aforementioned 2007/0109219,this method also requires judicious use of differential release sheetsto enable the second release sheet to be peeled from the double releasefilm without disturbing the first release sheet.

Construction Method C

As already indicated, a preferred ALP process of the invention involvesink jet printing on a lamination adhesive layer overlying anelectro-optic layer, which is itself already in position on a backplane.A preferred method for forming the lamination adhesive/electro-opticlayer/backplane intermediate structure, which minimizes the number oftimes the (typically) fragile backplane is laminated is as follows. Afirst release sheet/electro-optic material/lamination adhesive/secondrelease sheet structure is formed as described in Construction Method Babove. However, in this case, a second lamination adhesive layer iscoated on to a third release sheet, the first release sheet is removedand the electro-optic layer laminated to the second lamination adhesivelayer to form a double release film. One of the release sheets isremoved from this double release film and the remaining layers laminatedto a backplane. This method also requires judicious use of differentialrelease sheets.

One preferred form of the EOLP process of the present inventioncomprises the following steps:

-   -   (a) a layer of an encapsulated electrophoretic material or        polymer-dispersed electrophoretic material is coated on to a        backplane comprising at least one pixel electrode;    -   (b) a color filter array is printed directly on the        electrophoretic material layer using an ink jet printer;    -   (c) the electrophoretic material layer, color filter array and        backplane are dried in an oven to remove the volatile components        of the ink jet ink; and    -   (d) the electrophoretic material layer with the dried color        filter array thereon is laminated via a lamination adhesive to a        front substrate which provides a light-transmissive front        electrode for the final display and (normally) a protective        layer which supports and provides mechanical protection to this        front electrode, and optionally any desired barrier or        radiation-absorbing layers; this step is conveniently effected        by coating a layer of the lamination adhesive on a release        sheet, drying the lamination adhesive layer, laminating the        dried layer to the surface of the electrophoretic material        layer, peeling the release sheet and then laminating the        thus-exposed surface of the lamination adhesive to the front        substrate.

It is well known to those skilled in the technology of encapsulatedelectrophoretic media that, as described in some of the aforementioned EInk and MIT patents and applications, when an encapsulatedelectrophoretic medium, including a polymer-dispersed electrophoreticmedium, is coated on a smooth surface, such as the surface of a releasesheet, the resultant layer of electrophoretic medium has a smoothsurface facing the surface on which it is coated and a rough surface onits opposed side, the roughness of this surface being caused byshrinkage of the medium as it is dried or cured, and consequentprotrusion of capsule or droplets from the surrounding surface. Thepreferred process of the invention described above places the colorfilter array on the rough surface of the electrophoretic medium. If itis desired to form the color filter array on the smooth side of theelectrophoretic medium (which may, at least in some cases, result inmore precise printing of the color filter array), the electrophoreticmedium may be coated on a release layer, and laminated to a backplanewith lamination adhesive. (This is conveniently done in the mannerdescribed in the aforementioned U.S. Pat. No. 7,110,164 by coating theelectrophoretic medium on a first release sheet, coating the laminationadhesive on a second release sheet, laminating the two resultantstructures together with the lamination adhesive contacting theelectrophoretic medium, and thereafter peeling the second release sheetfrom the lamination adhesive; the two release sheets of course beingchosen so that this peeling can be effected without disturbing the firstrelease sheet.) After this lamination, the first release sheet isremoved from the electrophoretic medium and the color filter arrayprinted on the smooth side of the electrophoretic medium thus exposed.The remaining steps of the process are essentially unchanged.

A second preferred EOLP process of the invention, illustrated in theaccompanying drawings, can readily be applied to the production of anactive matrix display. The drawings are not strictly to scale; inparticular, the thicknesses of the various layers are greatlyexaggerated relative to the lateral dimensions of the layers. Theprocess begins as described in the aforementioned U.S. Pat. No.7,110,164 by coating an electrophoretic medium 12 on a first releasesheet 14, coating as thin a layer as possible of a lamination adhesive16 on a second release sheet 18, and laminating the two resultantstructures together with the lamination adhesive 16 contacting theelectrophoretic medium 12, to form the structure shown in FIG. 1.Thereafter, the second release sheet 18 is peeled from the laminationadhesive 16, and the remaining layers 12, 14 and 16 are laminated to anactive matrix backplane 20 provided with fiducial marks (not shown) toform the structure shown in FIG. 2. High precision registration is notrequired during this lamination.

The first release sheet 14 is then removed from the electrophoreticmedium 12, thus exposing the smooth surface of this medium, and a colorfilter array (indicated schematically as comprising red, green and bluecolor stripes 22R, 22G and 22B respectively in FIG. 3) is ink jetprinted on this smooth surface using a high precision ink-jet printerand positioning system relying upon the fiducial marks formed on thebackplane 22. In a manufacturing environment, this step is easilyautomated. Note that this technique avoids delicate alignment of apre-formed color filter array with the backplane, the positioning andalignment of the color filter array being controlled by the fiducialmarks formed on the backplane 22 itself. The fiducial marks themselvescan readily be located with high accuracy as part of the patterningprocedures used during manufacture of the backplane.

The color filter array is then dried by any convenient method, and afront substrate comprising a transparent electrode 24 and a supportlayer 26 is laminated over the color filter array by means of alamination adhesive 28, as shown in FIG. 4. For reasons discussed in theaforementioned 2007/0109219, the lamination adhesive 28 is desirablyrelatively conductive to provide the final display with good lowtemperature performance characteristics. Finally, if desired any barrierlayers 30 may be provided over the support layer 26 to provide moistureand oxygen barriers and ultra-violet radiation filtering. Edge seals mayalso be provided around the periphery of the display, as described forexample in the aforementioned U.S. Pat. No. 6,982,178.

Note that in both preferred EOLP processes of the present inventiondescribed above, the color filter array is formed on the electrophoreticmedium layer after that layer is already present on the backplane.Forming the color filter array in this manner avoids any problems causedby dimensional changes in an electrophoretic layer bearing a colorfilter array during lamination of such an electrophoretic layer to abackplane.

Typically, in the various processes of the present invention, it isdesirable that the colorant in the ink jet ink be confined as close aspossible to the surface of the layer to which it is applied. When theink jet ink is being applied to the electro-optic layer itself, suchconfinement is desirable not only because the surface of electro-opticlayer is where the colorant serves its color-controlling function, butalso because such confinement of the colorant renders it less likely tocompromise the electro-optic performance of the electro-optic layer. Inother processes, it is generally desirable to avoid the ink diffusingthrough the layer to which it is applied since such diffusion may causeintermixing of various colored areas and thus degradation of the colorshown on the display. The use of transparent pigmented inks is thereforepreferred. If dye-based inks are to be used, it may be desirable toinclude mordant polymers in the layer to which the ink is applied, forexample as a constituent of the binder in an encapsulatedelectrophoretic medium layer. Such mordant polymers contain groupscapable of binding otherwise soluble dyes and confining them to asurface portion of the ink-receiving layer. The preferred binders foruse in encapsulated electrophoretic media are typically anionicallycharged, and hence can be expected to act as mordants for cationic dyes,so cationic inks are preferred for use with such binders. Incorporationof metal ions into the ink-receiving layer may mordant suitable ink jetdyes or precursors by coordination of the metal. The resultingcomplexed, mordanted dyes frequently show enhanced stability againstphoto-degradation.

Most ink-jet inks, particularly those for use in inexpensive printersdesigned for home and small office use, contain substantial amounts ofhumectants, for example ethylene glycol, methoxy ethanol, glyme, andother similar hydrophilic species. These materials tend to bedeleterious in the present process, and their use should be minimized. Acommercial ink jet ink formulation can be produced with very muchsmaller humectant concentrations, since a major function of thesematerials is to prevent nozzle clogging caused by drying of the printerink. Ink jet inks with minimal amounts of humectants are preferred foruse in the present process. To the extent that humectants are necessary,volatile materials with minimal ability to swell the ink-receivinglayer, and especially the cell walls of encapsulated electrophoreticmedia, should be used.

Ink jet inks often contain surfactants, some of which may showdeleterious effects in electro-optic media, for example by affecting theswitching performance of encapsulated electrophoretic media, theinternal phases of which often contain surfactants carefully chosen tomaintain electrophoretic particle stability and switching performance.Anionic surfactants, particularly those with very low critical micelleconcentrations, appear to be particularly problematical in this respect.In any case, the surfactant type and concentration in the ink jet inkshould be optimized and minimized for the present process, and forcompatibility with electro-optic performance.

The following Examples are now given, though by way of illustrationonly, to show details of particularly preferred reagents, conditions andtechniques used in the processes of the present invention.

EXAMPLE 1

This Example illustrates an adhesive layer printing process of thepresent invention using Construction Method C described above.

An encapsulated electrophoretic medium was prepared comprisinggelatin/acacia capsules having an internal phase comprisingpolymer-coated titania white particles and polymer-coated copperchromite black particles in a hydrocarbon fluid. The capsules wereformed into a slurry using an aqueous polyurethane binder substantiallyas described in Example 4 of the aforementioned U.S. Pat. No. 7,002,728.The resultant capsule slurry was slot coated on to a loose release sheetand dried to form a loose release sheet/capsule layer sub-assembly.Separately, a custom polyurethane adhesive was coated on to a tightrelease sheet, and then laminated to the loose release sheet/capsuleslayer sub-assembly, with the adhesive layer contacting the capsulelayer. Separately, a polyacrylate adhesive was coated on to a looserelease sheet. The loose release sheet was peeled from the capsulelayer, and the exposed surface of the capsule layer laminated to thepolyacrylate adhesive on the loose release sheet, to form a doublerelease film having the following sequence of layers:

loose release sheet/polyacrylate adhesive/capsule layer/polyurethaneadhesive/tight release sheet.

From this double release film, there was laser cut a portion of a sizeappropriate for a 6.1 inch (155 mm) electrophoretic display. The looserelease sheet was peeled from the polyacrylate adhesive and theremaining layers of the double release film were laminated to a 6.1 inch(155 mm) thin film transistor active matrix backplane. The tight releasesheet was then peeled from the polyurethane adhesive to expose thesurface of this adhesive for ink jet printing.

The exposed polyurethane adhesive surface was then ink jet printed usinga Dimatix DMP-5000 Material Deposition Printer (available commerciallyfrom Fujifilm Dimatix, Inc., 2230 Martin Avenue, Santa Clara Calif.95050, United States of America) using 16 jet piezoelectric heads(available as disposable cartridges through Dimatix). Generally 2-3heads were used per print to improve jetting quality. The inks used wereSunjet Crystal UV curable ink in cyan (Crystal UDG U4970 Cyan Jet Ink),magenta (Crystal UDGU4896 Magenta Jet Ink), and yellow (Crystal UDGU4970 Yellow Jet Ink). A 30 μm drop spacing was used. The printed areaconsisted of 800 pixels in the x direction and 600 sub-pixels in the ydirection, each pixel being 153×151 μm. These pixels were overprintedtogether in groups of 4×600 pixels, forming a series of 0.612 by 90.4 mmbars (200 bars in total, 67 each cyan and magenta bars and 66 yellowbars).

The printer was charged and calibrated with a cyan print cartridge. Thebackplane/double release film was placed in the printer and a fiducialmark on the backplane was found using Dimatix optics and software. Thecyan bars were then printed. The printed backplane/double release filmwas then removed from the printer and bombarded with 20 W/inch (0.8W/mm) of ultraviolet radiation to cure the deposited ink. The processwas then repeated with magenta and yellow inks, each color being offsetby 0.612 mm in the x direction.

To complete the display, a 5 mil (127 μm) PET film bearing an ITOcoating on one surface was cut to the size needed for the display, andlaminated to the exposed, printed adhesive layer, with the ITO-coatedsurface in contact with the printed adhesive layer.

EXAMPLE 2

This Example illustrates a printed protective layer process of thepresent invention using Construction Method A above.

An encapsulated electrophoretic display was prepared by coating capsulessimilar to those described in Example 1 above on the ITO-coated surfaceof a PET/ITO film and drying, separately coating a custom polyurethaneadhesive on to a release sheet, and laminating the adhesive/releasesheet sub-assembly to the PET/ITO/capsule layer sub-assembly, with theadhesive contacting the capsule layer to form a front plane laminate.This front plane laminate was cut to size, the release sheet removed andthe remaining layers laminated to a thin film transistor active matrixbackplane to form a monochrome display. All the preceding steps werecarried out substantially as described in the aforementioned U.S. Pat.No. 6,982,178.

The display thus prepared was ink jet printed using the same printer andinks as in Example 1 above. Printing was effected using the arrangementshown in FIG. 5 of the accompanying drawings, in which a single pixel isrepresented by the 6×6 area within the heavily lined box. As may be seenfrom FIG. 5, the 6×6 pixel is anisotropic, comprising a 3×4 cyansub-pixel, a 3×4 magenta sub-pixel and a 6×2 yellow sub-pixel. Thispixel is tessellated to fill the entire display, with adjacent pixelsbeing inverted relative to one another in the vertical direction (asillustrated in FIG. 5) so that the repeating unit on the backplane, asshown in FIG. 5, was similar to the pixel unit but twice as large ineach direction.

The cyan sub-pixels were printed first as a matrix of 0.918 by 1.208 mmrectangles offset by 1.836 mm in the x direction and 2.416 mm in the ydirection. The display was removed from the printer and bombarded with20 W/in (0.8 W/mm) of ultraviolet radiation to cure the printed ink. Thesame pattern, offset by 0.918 mm in the x direction, was printed usingmagenta ink, followed by another curing step. Finally a series of yellowstripes 120.8 by 0.604 mm was printed in the remaining area and cured.

The present processes provide several major advantages:

(a) the processes can be used for rapid construction of prototype colordisplays, even active matrix displays, since the process is well adaptedfor “one-off” production and no expensive masks or similar devices arerequired for each new type of color filter array.

(b) no expensive pre-formed color filter array is required; the array isproduced on demand by printing directly on the desired layer. The costof the resulting display is greatly reduced as a result. This saving isparticularly important for larger displays.

(c) the optical performance of the display is not degraded because ofmultiple optical layers, as in the case of a separately constructed,laminated color filter array or overlay. Further, in many processes ofthe present invention intimate contact between the colorant and theimaging layer means that there is no optical degradation resulting fromparallax.

(d) the construction and manufacture of the color display is simplifiedbecause the alignment and application of the colored areas isfacilitated: it is easier to position the active matrix backplane usingfiducial marks built into that portion of the display than to align apre-formed color filter array with the backplane in two dimensions. Thismethod of construction would also be more amenable to flexiblebackplanes, since ink jet printing allows for correction for dimensionalchanges of the backplane during manufacture.

Numerous changes and modifications can be made in the preferredembodiments of the present invention already described without departingfrom the scope of the invention. Accordingly, the foregoing descriptionis to be construed in an illustrative and not in a limitative sense.

1. A process for preparing a layer of electro-optic material having acolor filter array thereon, which process comprises ink jet printing aplurality of colored areas on one surface of the layer of electro-opticmaterial.
 2. A process according to claim 1 wherein a plurality of firstcolored areas and a plurality of second colored areas are printed onsaid one surface of the layer of electro-optic material, the first andsecond colored areas being of different colors.
 3. A process accordingto claim 1 wherein the electro-optic material comprises a rotatingbichromal member material or a microcell electrophoretic material.
 4. Aprocess according to claim 1 wherein the electro-optic materialcomprises an encapsulated electrophoretic material comprising aplurality of capsules in a binder, or a polymer-dispersedelectrophoretic material.
 5. A process according to claim 1 wherein theink used is radiation curable and after the ink has been printed it isexposed to radiation effective to cure the ink.
 6. A process accordingto claim 1 wherein the ink used comprises pigment particles in anorganic solvent.
 7. A process according to claim 1 wherein the layer ofelectro-optic material is disposed on a backplane comprising at leastone pixel electrode.
 8. A process according to claim 1 furthercomprising laminating an adhesive layer over said one surface of thelayer of electro-optic material.
 9. A layer of electro-optic materialhaving a plurality of colored areas printed on one surface thereof. 10.A layer of electro-optic material according to claim 9 having aplurality of first colored areas and a plurality of second colored areasprinted on said one surface, the first and second colored areas being ofdifferent colors.
 11. A layer of electro-optic material according toclaim 9 wherein the electro-optic material comprises a rotatingbichromal member material or a microcell electrophoretic material.
 12. Alayer of electro-optic material according to claim 9 wherein theelectro-optic material comprises an encapsulated electrophoreticmaterial comprising a plurality of capsules in a binder, or apolymer-dispersed electrophoretic material.
 13. A layer of electro-opticmaterial according to claim 9 disposed on a backplane comprising atleast one pixel electrode.
 14. A layer of electro-optic materialaccording to claim 9 having an adhesive layer laminated over said onesurface of the layer of electro-optic material.
 15. An article ofmanufacture comprising, in order: a light-transmissiveelectrically-conductive layer; a layer of a solid electro-optic mediumin electrical contact with the electrically-conductive layer; anadhesive layer; and a release sheet, wherein the layer of a solidelectro-optic medium is a layer according to claim
 9. 16. An article ofmanufacture comprising: a layer of a solid electro-optic medium havingfirst and second surfaces on opposed sides thereof, a first adhesivelayer on the first surface of the layer of solid electro-optic medium; arelease sheet disposed on the opposed side of the first adhesive layerfrom the layer of solid electro-optic medium; and a second adhesivelayer on the second surface of the layer of solid electro-optic medium,wherein the layer of a solid electro-optic medium is a layer accordingto claim
 9. 17. An article of manufacture comprising: a layer of a solidelectro-optic medium having first and second surfaces on opposed sidesthereof, a first release sheet covering the first surface of the layerof solid electro-optic medium; and a second release sheet covering thesecond surface of the layer of solid electro-optic medium, wherein thelayer of a solid electro-optic medium is a layer according to claim 9.18. An article of manufacture comprising, in order: a release sheet; alayer of a solid electro-optic medium; an adhesive layer; and at leastone of a light-transmissive protective layer and a light-transmissiveelectrically-conductive layer, wherein the layer of a solidelectro-optic medium is a layer according to claim
 9. 19. A process forpreparing a sub-assembly useful for forming a color electro-opticdisplay, the process comprising providing a sub-assembly comprising alayer of electro-optic material and an adhesive layer having an exposedsurface, and ink jet printing a plurality of colored areas on theexposed surface of the adhesive layer.
 20. A sub-assembly useful forforming a color electro-optic display, the sub-assembly comprising alayer of electro-optic material and an adhesive layer, the adhesivelayer having a plurality of colored areas printed on one surfacethereof.
 21. A process for preparing a color electro-optic display, theprocess comprising providing a film comprising a layer of electro-opticmaterial and a protective layer having an exposed surface, and ink jetprinting a plurality of colored areas on the exposed surface of theprotective layer.
 22. A film for use in forming a color electro-opticdisplay, the film comprising a layer of electro-optic material and aprotective layer having an exposed surface, the protective layer havinga plurality of colored areas printed on its exposed surface.
 23. Aprocess for providing printed colored areas on an electro-optic display,the process comprising: providing a display comprising a backplanebearing a plurality of pixel electrodes and a layer of an electro-opticmaterial disposed on the backplane, the display having an exposedsurface remote from the backplane; applying voltages to the pixelelectrodes and thereby forming an image on the layer of electro-opticmaterial; detecting the image; and ink jet printing the colored areas onthe exposed surface in registry with the detected image.
 24. A processfor placing a color filter array on an electro-optic display, theprocess comprising: providing a color filter array; providing a displaycomprising a backplane bearing a plurality of pixel electrodes and alayer of an electro-optic material disposed on the backplane, thedisplay having an exposed surface remote from the backplane; applyingvoltages to the pixel electrodes and thereby forming an image on thelayer of electro-optic material; detecting the image; and securing thecolor filter array on the exposed surface in registry with the detectedimage.